With increasingly stricter air quality standards and with increasingly greater energy demand being experienced and the failure to satisfy this demand with oil, the coal reserves have become more and more attractive as a practically unlimited source of energy. However, many of the coal deposits are found with high sulfur content which has imposed a severe economic penalty on these coal deposits because of air quality requirements and thereby prevented the ready entry into the market of high sulfur content coal. A high sulfur content coal is defined as having greater than 0.5 to 1.0 percent by weight of sulfur in elemental or combined form. Although various methods have been tried for removal of sulfur from various grades of coal, economic considerations have also rendered these methods highly unattractive. Hence, a great endeavor has been made to convert coal directly into a usable fuel which would meet air quality standards. However, the best processes which are known to us remove considerable smaller percentage of sulfur from coal, only about half of that possible according to the present physical processes. Also, not all sulfur species found in coal are removed when practicing some of the prior art processes.
In upgrading coal, it must be remembered that a very high volume industrial commodity is being handled. For this reason, any process which requires upgrading of this material must be economically competitive, a viable alternative to other processes, and a process with little, if any, overall penalty, either associated with disposal problems or air quality problems.
Still further, the process by which coal is upgraded as distinguished for the process by which coal is used must by itself be such that it does not affect air quality standards or affect these to a considerably smaller degree than the overall benefit which is gained.